lomax



Feb. 22, 1944. c. E. LOMAX 22,442

- TELEPHONE SYSTEM Original Filed April 27, 1938 2 Sheets-Sheet 1 TRANS.

FIG. 1

W 00 1a 2 N N [II a 0.1

INVENTOR.

CLARENCE E. LOMAX 7 BY M z g ym 4, ATTORNEYS.

Reissued Feb. 22, 1944 UNITED STATES PATENT OFFICE TELEPHONE SYSTEMClarence Ernest Lomax, Oak Park, Ill., assignor to Automatic ElectricLaboratories, Inc., a corporation of Delaware Original No. 2,187,943,dated January 23, 1940, Serial No. 204,494, April 27, 1938. Applicationfor reissue August 23, 1940, Serial No. 353,988

31 Claims.

The present invention relates to telephone systems and more particularlyto improved telephone E. Lomax, granted June 21, 1927, it sometimesoccurs that one party located at a given substation may have occasion tocall the telephones of a particular group of other parties at frequentintervals. This is particularly true of an executive who relies upontelephone facilities to secure information from his immediatesubordinates. In a situation of this character, the delay incident tothe operation of a manual system or the labor incident to the operationof the calling device in automatic systems may prove burdensome to theparty initiating the calls. In order to simplify the calling operation,the improved direct call system disclosed in the abovementioned patentwas developed. This system is so arranged that calls between a number oftelephones may be initiated at a given substation through the simpleexpedient of selectively actuating calling keys individuallycorresponding to the telephones which are frequently called.

While the disclosed system of the above-mentioned patent is perfectlysatisfactory in operation and is an economical arrangement when a ratherlarge number of telephones make up the group to which calls arefrequently initiated, it is somewhat expensive to manufacture andinstall when used in a system wherein only a small number of telephonesubstations are to be arranged for direct call service.

It is an object of the present invention, therefore, to provide, in atelephone system, improved apparatus of the general character briefly described above which is exceedingly simple in arrangement, is reliable inoperation and is very inexpensive to manufacture and install in anyapplication where only a small number of telephone lines are to becalled from the special or executive substation.

It is another and more specific object of the invention to provide in anarrangement of the form briefly described above improved apparatus: forimpressing a warning signal on the line leading to a called substationin response to the initiation of a call at the special or executivesubstation at a time when the called substation is busy.

The invention is illustrated as being incorporated in an automatictelephone system wherein automatic switching equipment of the impulseresponsive type is provided for setting up connections between theplurality of lines of the system. The arrangement is such that theautomatic switching equipment is not utilized in the establishment ofconnections between one of the lines leading to the executive substationand the lines individually extending to the telephones which arefrequently called from the executive substation. Instead of using theregular automatic switching equipment, there is provided, at

the telephone station of the executive and for the purpose of permittingdirect calls to the frequently called subordinate lines, specialsubstation equipment which is utilized only on outgoing direct calls andis arranged to be connected by way of a link line to any one of thegroup of frequently called subordinate lines. More particu-' larly, linerelays are provided in individual as-' sociation with the lines of thelast-mentioned group. Each of the line relays is provided with anoperating circuit and includes contacts for connecting the associatedline to the link line by way of which connections are routed from theexecutive substation to the subordinate lines. Key operated switches areincluded in the special substation equipment, which individuallycorrespond to the relays and are selectively operable to complete therelay operating circuits. Associated with the aforementioned link lineare a plurality of common control relays, certain of which operate inresponse to the operation of 7 any one of the key switches and functionoperatively to connect the link line to the special substationequipment. There is also included in the common equipment a busy relaywhich is op-' erative in response to the selection of a busy one of thegroup of subordinate lines to prevent the last-mentioned control relaysfrom operating to connect the link line to the special substationequipment. This busy relay also functions to cause a background signalto be transmitted'over the selected busy line for the purpose ofinforming the party at the called substation that the executive at thespecial substation desires a con-- com-panying drawings in which Figures1 and v illustrate a telephone system having incorporated therein thefeatures of the present invention as briefly outlined above.

Referring now to the drawings, there is illustrated in Fig. 2 a portionof the equipment forming an automatic system of the type frequently usedto provide telephone facilities between the offices of a largemanufacturingorganization.

This type of system is commonly known as a private automatic exchange.In brief, the illustrated system comprises a plurality of substationlines, two of which are indicatedat 2H and 281, and automatic switchingequipment including a line switch 210, a selector switch 215 and aconnector switch 280 for setting up connections between the variouslines of the system. The line switch 210 and the other similar switchesare functions in response to switch control impulses,

transmitted thereto. It will be understood that the line switchesareindividually associated with the respective telephone lines and that aplurality of. numerical switches of each type, namely, a plurality ofselector switches and a plurality of connector switches are provided forperformingv the, l-ine switching and line selecting functions.

The numberofswitches of each type is, of course, determined by themaximum volume of trafiic the exchange i required to handle. Further inaccordance with conventional practice, each of the telephone linesterminating in the exchange is multipled to the corresponding bankcontacts of each of the connector switches, whereby a plurality ofselector and connector switches are available for setting'up connectionsbetween each line and every other line of the system,

The end of each telephone line remote from the automatic switchingequipment provided in the exchange terminates in a substation of theautomatic type, those associated with the lines 21! and 28! beingschematically indicated at A and B. respectively. In brief, each ofthese substations may comprise the usualhand set type of transmitter andreceiver, a cradle or hook switch, a ringer, and an impulsing device fortransmitting switch control impulses by way of the associated line tothe automatic switching eouipment located in the line terminatingexchange. Preferably, the elements of each substation icircuit areconnected and arranged to form the well-known anti-side-tone circuitvwhereby operation of the substation. transmitter does not causeoperation of the substation receiver.

Each of the line switches corresponding to and including the switch 211)may be of any conven tional arrangement. although preferably these levelof bank contacts and then rotated to bring the wipers into engagementwith a particular set of contacts in the selected level; vertical,rotary and release magnets; and control relays suitably connected andarranged to control the energization of the various magnets and th lineswitching in accordance With the particular functions to be performed bythe particular switch. Obviously, the particular arrangement of thecontrol apparatus embodied in the switches of diiferent type isdifferent in each instance depending upon the character of the switch.

As pointed out above, the present invention relates to the provision ofimproved apparatus whereby calls initiated at a particular substationmay be directly routed to certain of the lines terminating at theregular automatic switching equipment without operating a calling deviceconventionally used in automatic systems and without the delay incidentto the operations re quired to set up a connection in a manual system.To this end, there is provided at the executive or special substationthe improved substation apparatus shown in Fig. 1 and indicatedgenerally at mu. Connections may be routed directly from the substationequipment I!!!) to certain of the telephone lines terminating at theautomatic switching equipment, just described, through the :provision ofthe improved line connecting apparatus shown in Fig. 2 under the bracket285.. As explained in greater detail hereinafter, thespecial substationequipment I is only utilized on calls outgoing from the executive orspecial substation, this equipment being provided in addition to theregular substation equipment which is connected to a line terminating inthe regular automatic switching equipment of the automatic exchange inthe usual manner.

Neglecting for the present the substation equipment I00 and the lineconnecting apparatus .285 by way of which the equipment Hill may bedirectly connected to certain of the telephone lines provided in thesystem, the system as described above is more or less conventional inform and its operation is well understood in the art. Ii, for example, aparty at the substation A initiates a call to the substation B byremoving the receiver at the substation A from its supporting hook orcradle in the usual manner, a loop circuit is completed to the lineswitch 2m, causing this switch to operate to select an idle one of theselector switches corresponding to and including the selector switch215. Assuming that the switch 215, for example, is the first availableidle selector switch, when the line switch operates to the positioncorresponding to the trunk lines extending to this selector switch, itfunctions to switch the calling subscriber loop circuit through to theswitch 215 and to condition this selector switch to respond to theswitch control im ulses making up the first digit dialed at the callinsubstation. When the first-digit is dialed by the calling subscriber,the wiper carria e "structure embodied in the selector switch 215responds by elevating its wipers to position opposite the level of bankcontacts terminat-ina the group often trunk lines individually extending to the connector switches having access to the desired called line.In the present assumed case. the switch 215 elevate its wipers to aposition opposite the level of bank contacts terminating the trunk linesrespectively extendin to the connector switches in the group includingthe switch 280. Following the elevation of its wipers to this position,the selector switch 215 operates in the usual manner by rotating itswipers into engagement with the contacts terminating a trunk lineextending to an idle connector switch of the selected group. If it beassumed, for example, that the connector switch 280 is the firstavailable idle switch of the selected group, when the wipers of theswitch 215 are operated into engagement with the trunk line extending tothis connector switch, it further operates to switch the callingsubscribers loop circuit through to the connector switch and tocondition the connector switch to respond to the impulses of the secondand third digits dialed at the calling substation. The connector switch280 responds to the impulses of the second and third digits in the usualmanner by first elevating its wipers to a position opposite the level ofbank contacts terminating the group of ten lines including the desiredcalled line, and then rotating its wipers into engagement with the setof contacts terminating the desired called line 2!". The connectorswitch 286, like the other similar switches, is, in accordance withconventional practice, equipped to perform the usual auxiliary functionsof: testing the selected called line to determine the idle or busycondition thereof, returning busy tone over the calling line in theevent the selected line is found busy, and projecting ringing currentover the selected called line to actuate the signal device at the calledsubstation in the event the called line is idle at the time it istested. Assuming that the line 28I is idle, the ringing operation isinterrupted and the desired conversational circuit is completed when thecall is answered at the called substation B. Any desired arrangement ofthe connector switches may be used for insuring the release of theoperated switch train following the completion of the talking connectionby way thereof between the two subscribers lines. Thus, the apparatusembodied in the switch 28"?! may be arranged so that the release of theconnection is under the control of the calling party or, alternatively,under the control of the last party to hang up.

Referring now more particularly to the special substation equipment I00,this equipment comprises a transmitter I02, a translating device in theform of a loud speaker I03, a transformer or induction coil IM, animpedance matching transformer I05, a condenser I66, and the elements ofa balancing network I61, all interconnected to form a substation circuitof the well-known antiside-tone type. More particularly, the transformerI04 comprises two windings I68 and IE9, which are arranged to betraversed by audio frequency currents of equal magnitude and oppositephase during operation of the transmitter I52. The transformer IM alsoincludes a third winding I II] which is connected to the input terminalsof the loud speaker 13 and is preferably equally coupled to the twowindings H18 and I 38, so that alternating currents of equal magnitudeand opposite phase traversing the two windings Hi3 and I09 do not causevoltage of any substantial amplitude to be induced in the winding Miland the well-known anti-side-tone effect is realized.

The balancing network It! includes a plurality of impedance elementswhich are so proportioned and are so connected and arranged that themagnitude and phase angle of the equivalent impedance measured betweenthe terminals of the network and at all frequencies within the audiorange are respectively and substantially equal to the magnitude andphase angle of the equivalent impedance, measured between the two lineconductors CI50 and CIEI, of impedances external to the apparatus I andassociated with the line IflI when the apparatus HID is included in anestablished connection to one of the regular automatic telephone lines.larly, this balancing network is of the form described and claimed inthe co-pending application of Harold C. Pye, Serial No. 202,392, filedMay 16, 1938.

As explained in this co-pending application, when one substation isconnected by way of two relatively short subscribers lines and theautomatic switching equipment of an automatic exchange to a secondcalled substation, the predominant component impedances of theequivalent impedance of the circuit elements external to the first orcalling substation and measured at the terminals of the first or callingsubstation are those of the circuit elements necessarily provided at thecalled substation and of the coupling elements necessarily included inthe line connecting means located in the exchange by way of which theconnection is routed. Hence, to secure effective operation of theanti-side-tone circuit provided at the calling substation, it isnecessary to provide at this substation a balancing network whichincludes elements for balancing the effect of the circuit elements atthe distant substation and the coupling elements provided in the lineconnecting apparatus by way of which the connection is routed. To thisend, the balancing network I!" was developed, which network, brieflydescribed, comprises a resistor II3 for balancing the series resistanceof the line IIII and a second line extending to a called substation, acondenser II-I for balancing the capacitance of the coupling elementsincluded in the line connecting apparatus by way of which the connectionis established, and a series connected resistor H and condenser H6 forbalancing, respectively, the shunt resistance and the shunt capacitancebetween the line conductors of the two connecting lines. The networkfurther comprises a resistor II'I for balancing the eflect of thesubstation transmitter provided at the distant end of an establishedconnection, a condenser I I8 for balancing the effect of the condenser,corresponding to the condenser I06 and included in the transmissioncircuit at the distant substation, an induction coil II9 for balancingthe effect of the induction coil provided. at the distant substation,and an impedance I comprising an artificial receiver for balancing theeffect of the receiver located at the distant substation. The artificialreceiver or impedance I20 comprises a pair of L-shaped magnetic coremembers I2I and I22 having their adjacent ends or pole faces suitablymounted to provide air gaps therebetween which may be fixed at anydesired value to determine the impedance constants of the element.

Wound on the core members I2I and I22 are two there is also embodied inthe substation equip.

More particument I a plurality of key operated switches I25, I25 and I21which individually correspond to certain of the lines extending to theautomatic exchange and respectively include contact springs I28, I29 andI30. Each of the switches I25, 125, I21, etc., is of the locking typesuch that when operated to the off-normal position it remains in thisposition until it is manually restored to normal. More particularly,these switches are individually operable selectively to complete theoperating circuits for a plurality of line relays which are individuallyassociated with the lines of the group to which calls may be directlyforwarded from the substation equipment I00. Thus, the line connectingequipment 285 shown in Fig. 2 includes a pair of line relays R250 andR260 individually associated with the lines 28I and 21I, respectively,and having operating circuits which are arranged to be completed byoperation of the keys I25 and I26, respectively. Relays corresponding tothe two relays R252 and R250 are provided in association with each ofthe other lines of the system to which the substation equipment I00 isto have direct access. Each of the line relays corresponding to andincluding the relays R250 and R250 includes contacts for connecting theassociated line to a link line 212 by way of which the directconnections are established. This link line 212 has associated therewithcommon control apparatus comprising the seven relays, R200, R205, R2I0,R220, R230, R235 and R240. 0f the enumerated relays, the slow-to-releaserelay R240 is a lock-out relay, the slow-torelease relay R235 is a busytest relay, the slow-tooperate relay R220 is a line switching andringing relay, the slow acting relay R2I0 is a ring cut-on and lineswitching relay, the relay R205 is a back bridge or called party-answerrelay, the relay R233 is provided for the purpose of controlling theswitching relay R220, and the relay R200 is a calling-party-signalrelay. The auxiliary line connecting equipment shown in Fig. 2 alsoincludes a pair of coupling condensers 2H; and 211 which are providedfor the purpose of separating the talking loop extending to thesubstation equipment I00 from the talking loop extending to a calledsubstation, in the usual manner.

Referring now more particularly to the operation of the auxiliary lineconnecting equipment to establish a connection between the substationequipment I00 and a substation associated with one of the group ofsubordinate lines which are directly accessible to the equipment I00 andassuming, for example, that the call is intended for substation B, thecall is initiated by operation of the key switch I25 to its off-normalposition to complete the circuit for energizing the relay R250,corresponding to the called line 23L The circuit for energizing therelay R250 extends from ground by way of the springs I20, C140, RA254,R0255, the upper winding of R250, RAZM and the resistor 234 to battery.Upon operating, the relay R250 first completes a holding circuit foritself, which circuit extends by way of the grounded conductor C140,RA254, RA253, the lower winding of R250 and the winding of R240 tobattery. At RA254 and R0255, the relay R2 50, upon operating, opens apoint in its operating circuit as traced above. At RA256, the relay R250prepares a point in the common portion or the holding circuits, tracedhereinafter for R2I0 and R220, and completes a circuit extending by wayof RA256, C219, and RA230 for energizing R230. At RA25I, RA2-52 randRA251, the relay R250 connects the two line conductors C214 .and C213and the private conductor C216 of the link line 212 to the correspondingconductors of the selected called line 28I,.it being pointed out thatthe line and private conductors of the line ZBI as terminated in thebank contacts of the connector switch 280 are multipled to the indicatedcontact springs of the relay R250.

When the winding of R240 is energized inseries with the lower winding ofR250, the relay R240 operates to open, at RA24I, a point in the commonportion of the operating circuits of all of the line relayscorresponding to and including R250, R260, etc. Immediately R250operates, a test circuit including the winding of R235 is completed fordetermining the idle or busy condition'of the selected called line 28I.Whether or not the busy relayR235'operates depends upon the condition ofthe selected called line. More particularly, if the line ZBI is idle,battery potential is present on the control or private conductor C258thereof, Whereas if this line is busy, ground potential is present onthe control conductor C258. If it be assumed, for example, that theselected called line is busy when R250 operates, the relay R235 isenergized over the above-mentioned test circuit, which circuit extends bway of the grounded control conductor C258, RA252, C215, RA23I and itsassociated upper contact, and the winding of R235 to battery. Uponoperating, the busy relay R235 opens, at RA236, the above-traced circuitfor energizing R230. It is pointed out here that due to theslow-to-operate characteristic of R230, the relay R235 has suflicienttime to operate and open the operating circuit for R230 before thelast-mentioned relay operates when a selected called line is found busy.At RA239, the busy relay R235 applies ground to the ringing apparatusstart conductor C232, thereby to initiate the operation of the ringingapparatus, not shown, in a well-known manner. At .RA238, the busy relayR235, upon operating, completes a path for conducting busy tone currentby way of the line I'0I to the substation equipment I00. Specifically,this path extends from one terminal of the busy tone source, not shown,by way of C233, the condenser 229, RA238, CI5I, the winding 809, the twowindings of the transformer I05, the condenser I06, CI50, and the upperwinding of R200 to the opposite terminal of the bus tone source.Obviously, a portion of this current is also conducted from the lineconductor CI5I through the transformer windings I09 and I08 and thebalancing network I01 to the upper line conductor CI50. The inducedsignal voltage developed in the winding IIO as a consequence of the busytone current flowing through the windings I 08 and I09 is reproduced bythe loud speaker I03 to give the calling party an audible indicationthat the desired connection cannot immediately be obtained.

Since presumably the equipment I00 is provided at the telephone stationof an important official, calls originating at this substation areassumed to be important. In order, therefore, to indicate to the partiesconversing over a selected busy line that one of the parties is beingcalled from the executive telephone station, there is provided apparatusfor impressing upon the busy called line a background signal whichindicates that one of the two substations involved in the establishedconnection including the called line, is being called by a person at theexecutive telephone station. More particularly, when the busy relay R235operates, it completes a path for conducting ringing current by way ofthe called line to the called substation. The path of this currentextends from one terminal of the ringing current generator, not shown,by way of the condenser 228, RA231, C213, RA251, one side of the loopextending to the called substation B, the receiver at the calledsubstation, the other side of the established loop extending to thesubstation B and through the winding of one of the relays provided inthe operated switch train to the opposite terminal of the ringingcurrent source. The capacitance value of the condenser 228 is chosen sothat only a small current flows over the above-traced path, whereby theresulting signal is insufficient to interfere with the ensuingconversation, but is of sufficient strength to be heard by the party atthe called substation. Following the operation of the busy relay R235 toperform the functions just described, no further operation of theapparatus occurs until the operated switch I25 is restored to normal, torelease the partially completed connection in the manner pointed out indetail hereinafter. It will be apparent that even though the call failsbecause of the busy condition of the called line, a signal istransmitted to the called substation to indicate that this substation isbeing called from the executive telephone station. Hence the party atthe called telephone station B may, after finishing his conversationover the previously established connection, use the regular ex changefacilities to call the regular automatic substation, not shown, butprovided in the executive office where the apparatus I is located.

If it be assumed that the selected call line 28I is idle at the time theline relay R250 operates, the completion of the above-traced testingcircuit including the winding of the busy relay R235 does not result inthe operation of R235 for the reason that ground potential is notprescut on the control conductor C258. With R235 restored, the operatingcircuit for the relay R230 is held completed, so that R230 is caused tooperate a short interval following the operation of R250. Uponoperating, the relay R230 completes a circuit for energizing the upperwinding of the slow-to-operate relay R220, this circuit extending fromground by way of the upper winding of R220, RA23I and its associatedlower contact, C216 and RA252 to battery as extended to the controlconductor C258. The relay R220, upon operating, completes at RA223 aholding circuit for itself, this circuit extending by way of thegrounded conductor CI40, RA254, RA253, RA256, C219, RA223 and the lowerwinding of R220 to battery. At RA222, the relay R220 completes anobvious path for short-circuiting its upper winding and in so doingapplies ground to the control conductor C258, thereby to mark the calledline 2BI as busy in the bank contacts of the connector switches to whichthis line extends. This marking path extends from ground at RA222 by wayof RA23I, C216 and RA252 to the control conductor C258 of the line 28!.At RA226, the relay R220 applies ground to the ringing apparatus startconductor C232, whereby the ringing apparatus, not shown, is startedstation B. At RA225, the relay R220 completes a path for projectingring-back-tone current by way of the line IOI to the substationequipment I00, thereby to energize the loud speaker I03. The pathtraversed by the ringing current extends from one terminal of theringing current source, not shown, by way of the conductor C284, RA2I3,RA224, C213, RA251, one side of the line extending to the calledsubstation B, through the ringer or signal device at this substation,the other side of the line extending to the substation B, RA25l, C214,RA22I, RA2II and through the upper winding of the ring cut-off relayR2I0 to the opposite terminal of the ringing current source. The pathtraversed by the ring-backtone current is substantially the same as thattraversed by busy tone current and traced above, but extends by way ofthe ringing current conductor C284, the condenser 221, RA225, RA2I4, andRAEOI to the line conductor CI5I rather than by way of the conductorC233, the condenser 299 and RA238 traversed by the busy tone current.

The desired conversational connection is completed when the call isanswered at the called substation B. More particularly, when thereceiver at this substation is removed from its hook, a direct currentbridge is placed across the conductors of the line 28I in the usualmanner to complete a circuit for energizing the ring cutofi rela R2I0,this circuit extending from the grounded terminal of the ringing currentgenerator by way of 0284, RA2I3, RA224, C213, RA251, the bridge acrossthe line conductors of the line 28I at the called substation, RA25I,C214, RA22I, RA2I I and the upper winding of R2I0 to battery. When itsupper winding is energized over the above-traced circuit, the relay R2I0partially operates to complete at the X contacts associated with RA2I2 acircuit for energizing its two windings in series, this circuitextending by way of the grounded conductor CI40, RA254, RA253, RA256,C219, RA2I2 and the two windings of R2I0 in series to battery. At RA2IIand RA2I3 and their respectively associated resting contacts, the relayR2I0, upon fully operating, interrupts the ringing current path astraced above. At these same armatures and their respective workingcontacts, the relay R2I0 switches the called partys loop circuit throughto the two coupling condensers 2I6 and 2H, thereby to complete a circuitfor energizing the back ridge relay R205. At RA2I4 and its associatedlower contact, the relay R2I0 opens a point in the above-traced path forconducting ring-back-tone current to the substation apparatus I00. Whenenergized over the loop circuit extending to the substation B, the backbridge relay R205 operates to complete, at RA206, multiple holdingcircuits for the relays R2I0, R220 and R230. At RA201, the relay R205completes a circuit for energizing the relay R200, this circuitextending from ground at RA201 by way of the lower winding of R200,CI5I, the transformer windingsIllB and I I2, the transmitter I02, CI50and the upper winding of R200 to battery. Upon operating, the relay R200opens at RA20I, a point in the alternative circuit traced hereinafterfor projecting busy tone current over the loop extending to thesubstation apparatus I00. Following the operation of the relay R200, nofurther operation of the apparatus occurs until the operated key. switchI25, corresponding to the called line 28I, is manually restored to itsnormal position. It will be noted that talking battery is applied to theloop extending to the called substation I3" through the twdwindings'ofback relay R205 and that talking battery is applied to the loopextending to "the substation apparatus I90 through the'two windings oithe relay R200. Audio frequency signal currents incoming to thesubstation" apparatus I follow the exact bat s traced r e q s for th b son u ent in e a trave se t e wo nd ng 08 nd IQ? w eb e pqa me v a a enduced n t e'w 'n ne wh ch re reproduced y t e loudspeaker I03. Audiofrequency currents generated by operation of the transmitter I02 d liidhe nct n oint et e he t wi dings I08 and I09 and flow through thesewindings in opposite directions. By virtue of; the Provision of thebalancing network I01 the. CHI? rents traversing the winding I08 aresubstantially equal in magnitude and opposite in phase to thecorrespondin currents traversing the winding H10 at all frequenciesithin the audio range and, hence, no substantial portion of the audio.frequency energy developed by operation of the transmitter I02 isdelivered to. the loud speaker [03 for reproduction. Obviously, audiofre: quency currents roduced by operation of the transmitter I02 andtraversing the Winding. I09 are projected through the two couplingcondensers 215 and 2H to the loop circuit extending tothe calledsubstation B.

Following the. completion of a talking connection between the,substation apparatus I00 and the called substation B, the connectioncannot be released until after the called party hangs up.

,Thus, if the. operated key switch I25 is restored causing all of theserelays to restore. At RANT,

the. relayR205 opens a point in the above-traced operatingcircuitforR200, causing the last-mentioned relay to restore. Thus, the equipmentis entirelyreleased.

If. the called party at the substation B restores his receiver to itshook before the operated keyZ switch I25 is returned to its normalposition, the relay. R205 restores to open, at RAB, a point, in thecommon portion of the multiple holding circuits for R2--I0-, R220, R230,R240 and R250, but these relays are held operated over holding circuitscommonly including the grounded cone ductor Cl40. When R205 restores, itinterrupts, at RA20I, the above-traced operating circuit for R200,whereby the latter relay is caused to re.-. store. Upon restoring, therelay R200 completes, at RA20I, a circuit for projecting busy tonejour-v rent over the line IOI to the substation apparatus I00; This pathis similar to that traced previ-.

not been restored to normal. Obviously, when this key switch isreturnedto normal, the holding, circuits for five operated relays R2 I0,R220, R23 0,"

R nd, 25! ar nt rated au i a' eseiur y 9 restvre to condit on he o monequip e r is? f ther use he R2!" resto es it queue a BA? I 4 e p h 1Q!Pr e ti g b sy tone current over the line IM to the substation equip,rnent I00.

In order to release the common control appaa ratus following the partialoperation thereof; to Sel c nd s a usycall d e, it s n y n c a to es oro nqrma the, ke sw t correspondingto the called line, Thus, from thepreceding description it will be recalled that the three relays R235,R240 and R250 are energized andheld operated in response to theinitiation of a call to the substation B at a time when this substationis busy. Following the. receipt of busy tone, the calling party isexpected to restore the operated key switch I25 to, ncrrnal, thereby tocause the two relays R250 and R240 to restore, When R250 restores itbreaks, at RA252, the test circuitv over which R235 is being heldenergized causing the latterrelay to restore, to interrupt at R A238,and RAZSJ, respectively, the path for projecting busy tone current overthe line. I04; and thepath for projecting the background sig--. nalcurrent over the loop ei'itending to, the. called substation. When R235restores, thev common control apparatus is entirely released.

If a selected called line, as for example the line 2 8I is selected andtests busy, but the busy condition is renioved before the key switch,cor-- responding to the called line, is restored to nor-. mal, thedesired connection is established in the exact manner described above.More particu-. larly, if busying ground potential is, removed from C258.at a time when the. three. relays R235,

R240 and R250 are operated, the busy relayR235-L restores tointerruptthe busy tone current and the back-ground signal current paths,and to. recomplete, at RA236, the above-traced operate ing circuit forR230. Following the operation of 230, the four relays R220,- Rz u, R205and;

R200 operate in the manner and sequence described above, to complete thedesired convere sational connection.

It will be noted that during the release of the apparatus common to thelink line 212, the, re.-..

lay R240;is held operated for a, short time inter! val following therestoration of R250. So long; as

R240 is in its operated position, the operating circuits for all. of thelinarelays correspondingto, and including R250 and R260, are held openat, RAMI. The purpose of thisarrangement is. to, permit the operatedrelay R250-or any other operatedline. relay, fully to restore beforeanotherof the line relays operates, in responseto the operation ofanother of the, callingv key. switches to; apply ground to the,conductor C219; included in, the multiple holding circuit forR250 Bythis; arrangement, it is impossible for more than-011a of theline relayssimultaneously to be. lock 0P1. erated, irrespective of the speed withwhich one.

of the calling key switches is restored; and another key switch isoperated.

In View of the preceding description, it'willbe apparent thatconnections may be established to n n of h r f ub dinat e ine h:

theselective operation of the keys. I25, I26, I21, etc. Thus, the linerelays R250and R260, for example, are wired to the conductorsofthe linkline 212 and, associated with the control relay; equipment common tothis line in the same manner. Also, the mode of operation of; theapparatus to establisha connection to the line ZILLis, exactly the sameas. that just described with the, exception that; the; key, switch I25is, operated;

rather than the key switch I 25 and the relay R260, corresponding to theline 2', is caused to operate rather than the relay R250. Any number oflines may be included in the group of lines directly accessible to thesubstation apparatus Hill, although the greatest installation economy isrealized with the arrangement illustrated when the group of subordinatelines is not excessively large.

While there has been described What is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modifications may be made therein and it is contemplated in theappended claims to cover all such modifications as fall within the truespirit and scope oi the invention.

What is claimed is:

1. In a telephone system, a plurality of lines, automatic switchingequipment for setting up connections between said lines, a substation, alink line adapted to be utilized in a connection between said substationand any one of a group of said lines, relays individually associatedwith the lines of said group, each of said relays including contacts forconnecting the associated line to said link line, an operating circuitfor each of said relays, means comprising switches located at saidsubstation and individually corresponding to said relays for selectivelycompleting said operating circuits, and means including apparatusoperative in response to the operation of any one of said switches foreffectively connecting said link line to said substation.

2. In a telephone system, a plurality of lines,

automatic switching equipment for setting up connections between saidlines, a substation, a link line adapted to be utilized in a connectionbetween said substation and any one of a group of said lines, relaysindividually associated with the lines of said group, each of saidrelays including contacts for connecting the associated line to saidlink line, an operating circuit for each of said relays, a plurality ofswitches located at said substation and individually corresponding tosaid relays, each of said switches including contacts for completing theoperating circuit for the corresponding relay, and means includingapparatus operative in response to the operation of any one of saidswitches for effectively connecting said link line to said substation. I3. In a telephone syetem, a plurality of lines, automatic switchingequipment for setting up connections between said lines, a substation, alink line adapted to be utilized in a connection between said substationand any one of a group of said lines, relays individually associatedwith the lines of said group, each of said relays including contacts forconnecting the associated line to said link line, an operating circuitfor each of said relays, means comprising switches located at saidsubstation and individually corresponding to said relays for selectivelycompleting said operating circuits, and means including apparatusoperative in response to the operation of any one of said relays forefiectively connecting said link line to said substation.

4. In a telephone system, a plurality of lines, automatic switchingequipment for setting up connections between said lines, a substation, alink line adapted to be utilized in a connection between said substationand any one of a group of said lines, relays individually associatedwith the lines of said group, each of said relaysin-' cluding contactsfor connecting the associated line to said link line, an operatingcircuit for each of said relays, means comprising switches located atsaid substation and individually cor-' responding to said relays forselectively completing said operating circuits, and means including aplurality of relays successively operative in response to the operationof any one of said first-named relays for eifectively connecting saidlink line to said substation only in the event the line corresponding tosaid one relay is idle at the time said one relay operates.

5. In a telephone system, a plurality of lines, automatic switchingequipment for setting up connections between said lines, a substation, alink line adapted to be utilized in a connection between said substationand any one of a group of said lines, relays individually associatedwith the lines of said group, each of said relays including contacts forconnecting the associated line to said link line, an operating circuitfor each of said relays, means comprising switches located at saidsubstation and individually corresponding to said relays for selectivelycompleting said operating circuits, a plurality of relays including aringing relay, said plurality of relays being successively operative inresponse to the operation of any one of said first-named relays, a ringcut-off rela operative when a call to one of said group of lines isanswered and means comprising contacts controlled by said ringing relaand said ring cut-off relay for effectively connecting said link line tosaid substation.

6. In a telephone system, a plurality of lines, automatic switchingequipment for setting up connections between said lines, a substation, a

link line adapted to be utilized in a connection between said substationand any one of a group of said lines, relays individually associatedwith the lines of said group, each Of said relays including contacts forconnecting the associated line to said link line, an operating circuitfor each of said relays, a plurality of switches located at saidubstation and individuall corresponding to said relays, each of saidswitches including contacts for completing the operating circuit for thecorrespondin relay, and means including a plurality of relayssuccessively operative in response to the operation of any one of saidfirst-named relays fOr effectively connecting said link line to saidsubstation only in the event the line corresponding to said one relay isidle at the time said one relay operates.

7. In a telephone system, a plurality of lines, automatic switchingequipment for setting up connections between said lines, a, substation,a link line adapted to be utilized in a connection between saidsubstation and any one of a group of said lines, relays individuallyassociated with the lines of said group, each of said relays includingcontacts for connecting the associated line to said link line, anoperating circuit for each of said relays, a plurality of switcheslocated at said substation and individually corresponding to saidrelays, each of said switche including contacts for completing theoperating circuit for the corresponding relay, a plurality of relaysincluding a ringing relay, said plurality of relays being successivelyoperative in response to the operation of any one of said first-namedrelays, a ring cut-off relay operative when call to one of said group oflines is answered, and means comprising contacts controlled by saidringing relay and said ring cut-off relay for eftlon.

8.'In a telephone system, a plurality of lines, automatic switchinequipment for setting up connections between saidlines, a substation, a.link line adapted to. be, utilized in a connection between said;substation and anyone of agroup; of said lines, relays individuallyassociated with the; lines of said group, each: of said relays in-;.cluding: contacts for connecting; the associated line-to said link line,an operating circuit for each; of said relays, a plurality of switcheslocated at said substation and individually corresponding to .saidrelays, each of said switches including-contacts for completing theoperating circuit for the: corresponding relay, a plurality of relaysincluding a, ringing relay, said pluralit of relays being; successivelyoperative in response-to-the" operation of "anyone of said first-namedrelays,

a ring cut-01f relay operative when acall to one of said group oflinesis answered, means comprising'contacts controlled by said ringing relay:and'saidring cut-ofi relay for effectively connectlug-said link line tosaid substation, holdin circuit's;for said ringing and ring cut-offrelays, and

contactsindividually included in said switches for:

maintaining said holding circuits completed fol:- lowing the operationof said ringing and rin cut. offrelays.

9; In a telephone system, a plurality of lines, automatic switchingequipment for setting up: connections between said lines, a substation,a. link line adapted to be utilized in a connection between said"substation and any one-of a group. of. said, lines, relays individuallyassociatedv with the lines of said group, each ofsaid relays in cludingcontacts for connecting the associated. line'to saidlink line, anoperating circuit for each of said relays, a plurality of switcheslocated;- at" said substation and individually. correspondington saidrelays, eachof said switches including con tacts for completingtheoperating circuit for the: correspodning relay, a plurality of relayinclud"- ing a ringing relay, said plurality of relays beingsuccessively operative in response to the opera tion of any one of saidfirstnamed relays, aring cut-ofirelay operative when a call to oneofsaid group of lines is answered, means comprising contacts controlledby said'ringin relay and aid ring cut-off relay for efiectivelyconnecting said link line to said substation, a holding circuit for eachof said first-named relays, holding circuits for said'ringing and ringcut-offrelays, and contacts individually included in said switches:formaintaining the holding circuit of the corresponding first-namedrelay completed and" for maintaining'the holding circuits for saidringing and ring cut-off relays completedi 10. If a telephone system, apluralit of lines, automatic. switching equipment for setting upconnections between said lines, a substation, a

link line adapted to be utilized in a connection between said substationand anyone of a group" fectively' connecting said link line to saidsubstaatlng circuits fonall of said relays openfor a time of; anoperated the lines of said group, each of said relaysincluding'contactsfor'connecting the associated line to said" link line, an operating:circuit for each of said: relays, means comprising switches located atsaid substation and. individually corresponding to said relays for:selectively completing said operating circuits, means includingapparatus operative in response to the operation of any one of saidswitches for effectively connecting said link line to said substation,and means responsive to the. operation of any one of said relays forpre-' venting all of said relays from operating for ati nedntervalfollowing the restoration of theoperated. one of saidrelays.

12. In a telephone system, a plurality of lines, automatic switching.equipment for setting up connections between said lines, a substation,a" link line-adapted to be utilized in a connection between saidsubstation and any one of a group of said lines, relays individuallyassociated with thef'. lines of said group, each of said relays in-Cllldill'g contacts for connecting the associated line to said linkline, an. operating. circuit for each of. said relays, means comprising;switcheslocated" at said substation and individually corresponding: 1 tosaid relays, for selectively completing said operating circuits, meansincluding apparatus op erative in response to, the operatiorrof anyoneofsaid switches-for efiectively connecting said link line to saidsubstation, and means comprising a. slow-to-release relay operative inresponse to the operation of any one of said first-named'relays forholding the operating circuits for all of'said' first-named relays openfonatime interval follcwing the restoration of the. operated one of"said relays;

13. In a telephone'system', a. plurality of lines,

automatic switching equipment for setting up connectionshbetween saidlines, a substation, a. link line adapted to be utilized in aconnectionbetween said substation and anyoneofa group of said lines,relays individually. associated with the lines of said group, each ofsaid relays'in eluding contacts: for connecting the: associated line tosaid link. line;, an operating circuit for.

' each. of said relays, a plurality of switches located'; atsaidzsubstation and individually corre-- sponding tosaid. relays; eachof saidswitchessaid linkline to said substation only in the'event. theline. corresponding to" said one relay is idle at the time said onerelay operates, and means.

comprising a. slow-to-release relay operative in response to theoperation of-"any one of'said first.-

named relays forholdin'g the-operating circuits: or all of saidfirst-named relays open for a time interval. following the restorationofthe operated one ofsaid relays.

14: In a telephone system, a plurality oflines;

automatic switching equipmentter setting up" connection between saidlines; asubst'ation, a link line adapted to be utilized in atconnection=- between said substation and any one of a-group of saidlines, relays individually associated with the lines of said group, eachof said relays including contacts for connecting the associated line tosaid link line, an operating circuit for each of said relays, aplurality of switches located at said substation and individuallycorresponding to said relays, each of said switches including contactsfor completing the operating circuit for the corresponding relay, aplurality of relays including a ringing relay, said plurality of relaysbeing successively operative in response to the operation of any one ofsaid first-named relays, a. ring cut-off relay operative when a call toone of said group of lines is answered, means comprising contactscontrolled by said ringing relay and said ring cut-ofi relay foreffectively connecting said link line to said substation, and meanscomprising a slow-to-release relay operative in response to theoperation of any one of said first-named relays for holding theoperating circuits for all of said first-named relays open for a timeinterval following the restoration of the operated one of said relays.

15. In a telephone system, a plurality of lines, automatic switchingequipment for setting up connections between said lines, a substation, aplurality of switches at said substation, said switches individuallycorresponding to particular ones of a group of said lines, additionalswitching equipment controlled by said switches for selecting individuallines of said group for connection to said substation, and meansoperative in response to the selection of a busy one of said group oflines for transmitting a signal over the busy line.

16. In a telephone system, a plurality of lines, automatic switchingequipment for setting up connections between said lines, a substation, aplurality of switches at said substation, said switches individuallycorresponding to particular ones of a group of said lines, additionalswitching equipment controlled by said switches for selecting individuallines of said group for connection to said substation, said additionalswitching equipment including means operative in response to theoperation of one of said switches for establishing a connection betweensaid substation and the one of said group of lines corresponding to saidone switch, and means operative in response to the selection of a busyone of said group of lines for preventing said last-named means fromoperating and for transmitting a signal over the busy line.

17. In a telephone system, a plurality of lines, automatic switchingequipment for setting up connections between said lines, a substation, aplurality, of switches at said substation, said switches individuallycorresponding to particular ones of a group of said lines, additionalswitching equipment controlled by said switches for selecting individuallines of said group for connection to said substation, said additionalswitching equipment including means operative in response to theoperation of one of said switches for establishing a connection betweensaid substation and the one of said group of lines corresponding to saidone switch, and means comprising a busy relay operative in response tothe selection of a busy one of said group of lines, said busy relaybeing operative to prevent said last-named means from operating, totransmit a busy signal to said substation and to transmit a signal overthe busy line.

18. In a telephone system a plurality of lines,

automatic switching equipment for setting .111.) connections betweensaid lines, a substation, a link line adapted to be utilized in aconnection between said substation and any one of a group of said lines,relays individually associated with the lines of said group, each ofsaid relays including contacts for connecting the associated line tosaid link line, an operating circuit for each of said relays, meanscomprising switches located at said substation and individuallycorresponding to said relays for selectively completing said operatingcircuits, whereby particular lines of said group may be selected forconnection to said substation, and means operative in response to theselection of a busy one of said group of lines for transmitting a signalover the busy line.

19. In a telephone system, a plurality of lines, automatic switchingequipment for setting up connections between said lines, a substation, alink line adapted to be utilized in a connection between said substationand any one of a group of said lines, relays individually associatedwith the lines of said group, each of said relays including contacts forconnecting the associated line to said link line, an operating circuitfor each of said relays, means comprising switches located at saidsubstation and individually corresponding to said relays for selectivelycompeting said operating circuits, means including apparatus operativein response to the operation of one of said relays for establishing aconnection includin said link line between said substation and theselected line corresponding to the operated one of said relays in theevent the selected line is idle, and means operative in the event theselected line is busy for preventing said last-named means fromoperating and for transmitting a signal over the selected line.

20. In a telephone system, a plurality of lines,

automatic switching equipment for setting up connections between saidlines, a substation, .a link line adapted to be utilized in a connectionbetweensaid substation and any one of a group of said lines, relaysindividually associated with the lines of said group, each of saidrelays including contacts for connecting the associated line to saidlink line, an operating circuit for each of said relays, meanscomprising switches located at said substation and individuallycorresponding to said relays for selectively completing said operatingcircuits, means operative in response to the operation of one of saidrelays for establishing a connection including said link line betweensaid substation and the selected line corresponding to the operated oneof said relays in the event the selected line is idle, and meanscomprising a busy relay operative in the event the selected line is busyfor preventing said lastnamed means from operating, for transmitting abusy signal to said substation and for transmitting a signal over thebusy line.

21. In an intercommunication system, a Inaster station, a subordinatestation connected to a central office line, means including anintercomrnunicating line for routing a connection from said masterstation to said subordinate station, a signal at said subordinatestation and means for operating said signal in the event saidsubordinate station is occupied with a call involving said centraloflice line.

22. In an intercommunication system, a master station, a subordinatestation connected to a central oflice line, means including anintercommunicating line for routing a connection from.

said master station to said subordinate station, and means fortransmitting a Signal over said centra1 office line in the event saidsubordinate station is occupied with a call involving said central'ofiice line.

23. In an intercommunication system, a master station, a subordinatestation connected to a central oifice line, means including anintercommunicating line for routing a connection from said masterstation to said subordinate station, and means for transmitting signalsto both of said stations in the event said subordinate station isoccupied with a'call involving said central oflice line.

24. In a telephone system, a plurality of lines, means for setting upconnections between said lines, a station, additional means controllablefrom said'sta'tion for selecting any one of a group of said lines forconnection to said station, and means operative in response to theselection or a busy one of said group of lines for transmitti'n'g'asignal over the busy line. 7 25. In a telephone system, a plurality oflines,

means for setting up connections between said lines, a station,additional means controllable from said station for selecting any one ofa group of said lines for connection to said station, and me'ansoperative in response to the selection of a busy one of said group oflines for transmitting a signal to said station and for transmitting asignal over the busy line.

ordinate station for operating said signal.

27. In a combined telephone and loud-speak- "ing intercommunicatingsystem, 'a master station,

"a subordinate station, an intercommunicating line interconnecting saidstations, a signal at said master "station "and means controlled oversaid intercommunicating line jointly from said master station and saidsubordinate station for operating said signal.

28. In a combined telephone and loud-speaking intercommunicating system,a first station, a second station, an intercommunicating lineinterconnecting said stations, a signal at one of said stations, andmeans controlled over said intercommunicating line jointly from bothsaid stations for operating said signal.

29. In a combined telephone and loud-speaking intercommunicating system,a calling station having a distant talking transmitter, a calledstation, a source of supply current for said transmitter, anintercommunicating line interconnecting said stations, a switch at saidcalling station for connecting said source of current to saidint'er'communicating line, and means under the control'of said calledstation when said switch is operated for connecting said source ofsupply current to the transmitter at said calling station, said meansbeing controlled over said intercommunicating line.

30. In a combined telephone and loud-speaking intercomrnunicatingsystem, a calling station having a distant talking transmitter, a calledstation, a source of supply current for said transmitter, anintercommunicating line interconnecting said stations, means including aswitch at said calling station for connecting said source of current tosaid intercommunicating line, and means under the control of said calledstation when said switch is operated for connecting said source ofsupply current to the transmitter at said CLARENCE ERNEST

